1 files changed, 64 insertions, 0 deletions
diff --git a/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceRuntime.swift b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceRuntime.swift
new file mode 100644
index 0000000000..9ae62d1667
--- /dev/null
+++ b/third_party/rust/uniffi_bindgen/src/bindings/swift/templates/CallbackInterfaceRuntime.swift
@@ -0,0 +1,64 @@
+fileprivate extension NSLock {
+    func withLock<T>(f: () throws -> T) rethrows -> T {
+        self.lock()
+        defer { self.unlock() }
+        return try f()
+    }
+}
+
+fileprivate typealias UniFFICallbackHandle = UInt64
+fileprivate class UniFFICallbackHandleMap<T> {
+    private var leftMap: [UniFFICallbackHandle: T] = [:]
+    private var counter: [UniFFICallbackHandle: UInt64] = [:]
+    private var rightMap: [ObjectIdentifier: UniFFICallbackHandle] = [:]
+
+    private let lock = NSLock()
+    private var currentHandle: UniFFICallbackHandle = 0
+    private let stride: UniFFICallbackHandle = 1
+
+    func insert(obj: T) -> UniFFICallbackHandle {
+        lock.withLock {
+            let id = ObjectIdentifier(obj as AnyObject)
+            let handle = rightMap[id] ?? {
+                currentHandle += stride
+                let handle = currentHandle
+                leftMap[handle] = obj
+                rightMap[id] = handle
+                return handle
+            }()
+            counter[handle] = (counter[handle] ?? 0) + 1
+            return handle
+        }
+    }
+
+    func get(handle: UniFFICallbackHandle) -> T? {
+        lock.withLock {
+            leftMap[handle]
+        }
+    }
+
+    func delete(handle: UniFFICallbackHandle) {
+        remove(handle: handle)
+    }
+
+    @discardableResult
+    func remove(handle: UniFFICallbackHandle) -> T? {
+        lock.withLock {
+            defer { counter[handle] = (counter[handle] ?? 1) - 1 }
+            guard counter[handle] == 1 else { return leftMap[handle] }
+            let obj = leftMap.removeValue(forKey: handle)
+            if let obj = obj {
+                rightMap.removeValue(forKey: ObjectIdentifier(obj as AnyObject))
+            }
+            return obj
+        }
+    }
+}
+
+// Magic number for the Rust proxy to call using the same mechanism as every other method,
+// to free the callback once it's dropped by Rust.
+private let IDX_CALLBACK_FREE: Int32 = 0
+// Callback return codes
+private let UNIFFI_CALLBACK_SUCCESS: Int32 = 0
+private let UNIFFI_CALLBACK_ERROR: Int32 = 1
+private let UNIFFI_CALLBACK_UNEXPECTED_ERROR: Int32 = 2